Physicochemical, structural and volatile changes of soybean protein isolate induced by hydroxyl radical generating system

The aim of the study was to investigate the effect of hydroxyl-radical on soybean protein isolate (SPI) properties. SPI were incubated with different H ₂ O ₂ concentrations of 0, 0.1, 1, 5, 10 and 15 mM for 24 h. The oxidization induced more porous microstructure in SPI surface. The total sulfhydryl group, water/oil holding capacity (WHC/OHC), enthalpy, solubility of SPI with increasing the concentration of H ₂ O ₂ decreased significantly ( p < 0.05), while H ₂ O ₂ prompted a significantly increase in protein carbonyl content ( p < 0.05). FTIR confirmed that oxidation resulted in the gradual loss of α-helical and β-sheet structures with the concomitant increase of β-turn and random coil structures. Compared with the raw SPI, the moderate H ₂ O ₂ concentration (1 mM) enhanced emulsifying properties while lower (0.1 mM) and higher (5 mM) H ₂ O ₂ concentration significantly increased the foaming properties and the value of zeta potential, respectively ( P < 0.05). With the increase of H ₂ O ₂ concentration, the intensities of volatile compound were strongly influenced by the oxidation levels of SPI, some compounds increased, some decreased, which was likely owing to the structure changes of modified SPI. All in all, these results offered evidences of how protein oxidation affected the properties and structure of SPI.